Conventional television antennae are generally quite bulky and unsightly. In order to achieve best performance, outdoor antennae are preferred, for example, roof mounted antennae. However, these can be inconvenient to mount securely, and difficult to maintain. In the event of a storm, an outdoor antenna may easily become misaligned, or it may suffer damage.
Indoor antennae are commonly smaller than outdoor antennae for aesthetic reasons. However, their small size limits their efficiency, which means that they are generally suitable for reception only in areas where the television signals are strong. A tuned Yagi antenna has additional elements to increase gain, but this achieves high gain only along the front-rear direction of the antenna. Thus the antenna is highly directional and is also susceptible to receiving rear-reflected signals to cause ghosting. Typically the acceptance angle of a Yagi antenna is only about 20 degrees.
The present invention is concerned with providing an antenna of planar elements of compact size, disposed in different planes with increased gain for domestic television reception and reduced directional preference.
According to the invention, there is provided an antenna as claimed in claim 1 or claim 23 hereinafter. This provides a high gain antenna which has a wide range of acceptance angles. Further features of the invention are set forth in the dependent claims.
When referring to planes, a first plane differs from a second plane through orientation of the first plane with respect to the second plane. A plane offset vertically or horizontally from and parallel to a plane is considered to be the same plane as the plane from which it is offset.
The planes on which the respective lands are disposed may be orthogonal for optimal gain across a wide range of acceptance angles.
The provision of further lands in one or more planes may optimise antenna performance.
The shape of each land may be configured to optimise performance. Disposal of the lands symmetrically about an imaginary line may improve performance.
The first pair of lands may be integrated with or within a television. The second pair of lands may be mounted on a television wall bracket or within or on a television stand. This allows the first and second lands to maintain their orientations with respect to one another, and to be obscured from view during use.
The sheet material may be flexible (e.g. of plastics material) or it may be relatively rigid, for example a stiff cardboard sheet.
The electrically conductive foil type lands may be formed by a variety of means (e.g. printing, laminating, etching, evaporation), but preferably they are formed of foil (e.g. aluminium foil) hot pressed onto the sheet material.
A preferred antenna according to the invention, for use with a domestic television receiver, will now be described by way of example with reference to the accompanying drawing. The drawing shows the antenna in perspective view.
The antenna comprises a sheet 1 of stiff cardboard in the XY plane to which has been laminated by hot foil blocking four spaced aluminium foil lands 3,5,7 and 9. The aluminium foil is approximately 200×10−10 metres in thickness, which gives an electrical resistance of about 1.5 ohms per square. The foil is overcoated with an electrically-insulating lacquer.
The arrangement may be manufactured by sputtering aluminium to the desired thickness onto a lacquer-coated backing surface. The aluminium is then coated with adhesive and the combination hot foil blocked onto the sheet 1 with the adhesive adjacent the sheet. The backing surface is peeled away to leave the sheet 1, lands 3, 5, 7, 9 and lacquer overcoating bonded together.
Each pair of lands 3,5 and 7,9 is spaced apart from and is symmetrical about an imaginary line y-y on sheet 1.
The antenna also comprises additional lands 11, 13 disposed symmetrically about the imaginary line y-y in the XZ plane.
Lands 15, 17, 19, 21 may also be disposed in the XZ plane in addition to or in place of lands 11, 13. Lands 15, 17, 19, 21 are also disposed symmetrically about the imaginary line y-y. These lands may also be formed by laminating aluminium foil lands by hot foil blocking onto stiff cardboard. The aluminium foil is approximately 200×10−10 metres in thickness, which gives an electrical resistance of about 1.5 ohms per square. The foil is overcoated with an electrically-insulating lacquer. The arrangement may be manufactured by sputtering aluminium to the desired thickness onto a lacquer-coated backing surface. The aluminium is then coated with adhesive and the combination hot foil blocked onto the sheet with the adhesive adjacent the sheet. The backing surface is peeled away to leave the sheet, lands 15, 17, 19, 21 and lacquer overcoating bonded together.
Lands 11, 13 are located approximately a distance of λ/2 from sheet 1 along the Z axis. Additional/alternative lands 15, 17, 19, 21 approximately a distance of λ/2 from sheet 1 along the Y axis. λ is the wavelength of operation in the range of 500 to 900 MHz.
Feeds are taken from lands 3, 5 for obtaining a television signal in the range of 500 to 900 MHz.
The feed (not shown) to lands 3,5 preferably comprises a clip which presses a pair of strip conductors down onto the lacquer at adjacent corners of the lands 3,5. The contact to the aluminium foil is capacitive through the intervening lacquer (it can also be a direct metal-to-metal contact, without intervening lacquer). Alternative feeds are, of course contemplated and within the scope of the invention.
Lands 3,5 each have a maximum y-dimension of 20 cm and a maximum x-dimension of 20 cm. Lands 7,9 have a maximum y-dimension of 20 cm and a maximum x-dimension of 20 cm. At their closest approach lands 3,5 are spaced from lands 7,9 by 1 cm in the x-direction. Lands 3, 5 and 7, 9 are spaced-apart in the y-direction by 1 cm.
Lands 3, 5, 7 ,9 as shown may have a fully or partially tapered edge from the y side to the x side. The configuration of the tapered edge can be varied to optimise performance. Other configurations include substantially square or trapezoidal.
Lands 11, 13 each have a maximum x-dimension of 20 cm and a maximum z-dimension of 20 cm. Lands 15, 17, 19, 21 each have a maximum x-dimension of 20 cm and a maximum z-dimension of 20 cm.
Shorting the non-fed pair(s) of lands (7, 9, 11, 13, 15, 17, 19, 21) can improve band selectivity, and this can be achieved by shorting across a small area of exposed foil on each land.
In one embodiment, the antenna is designed for use through orientating the sheet 1 vertically within or on a television. Lands 11, 13 and 15, 17, 19, 21 preferably will be integrated with a television wall bracket and television stand respectively. Lands 11, 13 and/or lands 15, 17, 19, 21 are orientated with respect to sheet 1 in the range of 0 to 180°,preferably 45 to 135°,and most preferably 90°. When lands 11, 13 and/or lands 15, 17, 19, 21 are orientated orthogonally to sheet 1, they act as non-fed parasitic reflector lands along with lands 7, 9. It has been found that when lands 7, 9, 11, 13 and/or 15, 17, 19, 21 resonate in conjunction with the fed lands, an antenna with high gain and reduced directional preference is achieved.
Changing the planes in which the lands are located with respect to one another varies antenna output. For example, although lands 11, 13 and 15, 17, 19, 21 are disposed in the ZX plane, they may also be disposed in the XY plane. Alternatively, only lands 11, 13 may be disposed in the XY plane, or only lands 15, 17, 19, 21 may be disposed in the XY plane. In these arrangements, the lands 11, 13 and 15, 17, 19, 21 would be disposed along the imaginary line, but positioned so that they are symmetrical about the imaginary line. A greater or fewer number of lands can be used other than that shown to vary antenna output. Although, elements 3 and 5 are shown as the fed elements, in principle any or any combination of the lands shown can be fed.
In a further embodiment which is a variant of that illustrated, any or all of the land pairs 7 and 9, 11 and 13, 15 and 17, 19 and 21 are merged to form one contiguous land disposed symmetrically about the imaginary line y-y in the XZ plane, to act as parasitic reflectors to lands 3 and 5.
The shape and dimensions of the lands can be varied according to the frequency of operation to optimise antenna output at the frequency of operation.
Although the lands are described as being formed by laminating aluminium foil lands by hot foil blocking onto stiff cardboard, it is possible to use lands in the form of thin electrically conductive materials such as aluminium manufactured to present as foil type lands. In addition the foil type lands can be manufactured from microwave materials by selecting a material with the appropriate properties such as dielectric constant, thickness and conductor type. Hence, use of the word foil is used to mean both lands formed from a foil and lands formed in other ways which present similarly in the form of foil type elements. Lands of these types may also be integrated with a television, television wall bracket and/or television stand. The structure of these lands makes it practical to deploy the elements internally and/or externally on the television, television wall bracket and/or television stand.
It will be appreciated that this description is by way of example only; alterations and modifications may be made to the described embodiment without departing from the scope of the invention as defined in the claims.